Molded leadframe substrate semiconductor package

ABSTRACT

A process for forming semiconductor packages includes partially etching a leadframe matrix, encapsulating it with mold compound, placing a semiconductor die in a leadframe unit and singulating the leadframe matrix. A system for forming semiconductor packages includes means for partially etching a leadframe matrix, means for encapsulating it with mold compound, means for placing a semiconductor die in a leadframe unit and means for singulating the leadframe matrix.

This application is a Divisional Application of the co-pendingapplication Ser. No. 12/287,174, filed Oct. 6, 2008, now issued as U.S.Pat. No. 7,790,512, and titled MOLDED LEADFRAME SUBSTRATE SEMICONDUCTORPACKAGE,” which in turn claims priority of U.S. Provisional Patentapplication 61/002,138 filed Nov. 6, 2007, entitled “FRAME DESIGN ANDMOLD DESIGN CONCEPT FOR MOLD DESIGN THICKNESS,” both of which are herebyincorporated in their entirety.

RELATED APPLICATIONS

This application claims benefit of priority under 35 U.S.C. section119(e) of co-pending U.S. Provisional Patent Application 61/002,138filed Nov. 6, 2007, entitled FRAME DESIGN AND MOLD DESIGN CONCEPT FORMOLD DESIGN THICKNESS which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is in the field of semiconductor packaging and ismore specifically directed methods of achieving optimum thicknesses forsemiconductor packages.

BACKGROUND

In Leadframe Based Packaging, a leadframe matrix 100 in FIG. 1 isprocessed by placing singulated semiconductor die (not shown) into eachindividual leadframe unit 110. Then, bond pads on the die are wirebonded to an output pin 115 in the leadframe unit to effectuate adesired landing pattern onto a printed circuit board (not shown). Next,a mold compound is formed over the leadframe matrix 100 and allowed toset. Individual devices are marked, and the leadframe matrix issingulated by saw or other cutting apparatus into individualsemiconductor devices. Although this process is well known, it does notallow for control of the thickness of the final package. The thicknessof semiconductor devices is typically is dictated by the thickness ofthe die added to the thickness of the leadframe plus the mold compound.In certain applications, thinner semiconductor devices are desired. Whatis needed is a process and system for forming semiconductor leadframepackages with different desired thicknesses.

SUMMARY OF THE DISCLOSURE

One aspect of the invention is for a process of forming individualpackaged semiconductor devices. To that end, a leadframe matrix has athickness, a top surface and a bottom surface. At least one of the topsurface and bottom surface is etched to form a selectively half etchedleadframe having an etched pattern. The selectively half etchedleadframe is mounted onto a tape carrier and then the selectively etchedleadframe is encapsulated in a first mold compound such that the etchedpattern is filled with mold compound. As a result, a selectively halfetched molded leadframe is formed. At least one semiconductor device ismounted in at least one individual leadframe. The tape carrier isremoved and the selectively half etched molded leadframe is singulatedthereby forming individual packaged semiconductor devices. In someembodiments, the selectively half etched leadframe is encapsulated in afirst mold compound by placing the selectively half etched leadframebetween a top mold, having a film gate, and a bottom mold. A moldcompound is injected in a liquid state through the film gate such thatit encapsulates the selectively half etched leadframe thereby forming aselectively half etched molded leadframe. Alternatively, The selectivelyhalf etched leadframe can be encapsulated in a first mold compound byplacing the selectively half etched leadframe between a top mold, havinga pincer gate, and a bottom mold. Again, a mold compound in a liquidstate is injected through the pincer gate such that it encapsulates theselectively half etched leadframe thereby forming a selectively halfetched molded leadframe. In some embodiments, the top mold furthercomprises a vacuum pipe output. The process further comprises forming anear vacuum at the vacuum pipe to effectuate distribution of the firstmold compound. In some embodiments, the process of further comprisesencapsulating the selectively half etched molded leadframe in a secondmold compound. Also, mounting at least one semiconductor devicecomprises mounting the at least one semiconductor device on theselectively half etched molded leadframe and wirebonding such that theat least one semiconductor device is encapsulated by the second moldcompound. Alternatively, mounting at least one semiconductor devicecomprises mounting the at least one semiconductor device in a cavitywithin the individual leadframe and wirebonding such that the first moldcompound encapsulates the at least one semiconductor device.

In another aspect of the disclosure, a system of assembling asemiconductor package comprises means for selectively etching at leastone of a top surface and a bottom surface of a leadframe matrix. Thesystem also has a means for mounting the selectively half etchedleadframe onto a tape carrier annd means for encapsulating theselectively half etched leadframe in a first mold compound such that theetched pattern is filled with mold compound, thereby forming aselectively half etched molded leadframe. Also, the system has a meansfor mounting at least one semiconductor device in at least oneindividual leadframe, means for removing the tape carrier, and means forsingulating the selectively half etched molded leadframe thereby formingindividual packaged semiconductor devices. In some embodiments, themeans for encapsulating the selectively half etched leadframe in a firstmold compound has a means for placing the selectively half etchedleadframe between a top mold, having a film gate, and a bottom mold. Ameans for injecting a mold compound in a liquid state through the filmgate provides the mold compound such that it encapsulates theselectively half etched leadframe thereby forming a selectively halfetched molded leadframe. Alternatively, the means for encapsulating theselectively half etched leadframe in a first mold compound comprisesplacing the selectively half etched leadframe between a top mold, havinga pincer gate, and a bottom mold. A means for injecting a mold compoundin a liquid state through the pincer gate provides the mold compoundsuch that it encapsulates the selectively half etched leadframe therebyforming a selectively half etched molded leadframe. In some embodiments,the top mold further comprises a vacuum pump output and the systemfurther comprises means for forming a near vacuum for effectuatingdistribution of mold compound.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of theinvention are set forth in the following figures.

FIG. 1 shows a standard leadframe matrix.

FIG. 2 shows two portions of half etched leadframe matrices from top andcross sectional views.

FIG. 3A is a process of forming a molded half etched leadframe per anembodiment of the current invention.

FIG. 3B shows another view of the process of forming a molded halfetched leadframe of FIG. 3A.

FIG. 3C shows a process of forming a molded half etched leadframe per analternative embodiment of the current invention.

FIG. 3D is another view of the process of forming a molded half etchedleadframe of FIG. 3C.

FIG. 4 shows alternative half etched leadframe matrices from top andcross sectional views.

FIG. 5A shows an alternative process of forming a molded half etchedleadframe.

FIG. 5B shows an alternative process of forming a molded half etchedleadframe.

FIG. 5C shows an alternative process of forming a molded half etchedleadframe.

FIG. 5D shows an alternative process of forming a molded half etchedleadframe.

FIG. 6 is a process of applying the half etched leadframe to assemblesemiconductor packages.

FIG. 7 is an alternative process of applying the half etched leadframeto assemble semiconductor packages.

DETAILED DESCRIPTION

In the following description, numerous details and alternatives are setforth for purpose of explanation. However, one of ordinary skill in theart will realize that the invention can be practiced without the use ofthese specific details. In other instances, well-known structures anddevices are shown in block diagram form in order not to obscure thedescription of the invention with unnecessary detail. For example, it iscommonly known in the art of semiconductor device assembly that assemblyis generally done on a matrix array of leadframes, often referred to asleadframe strips, each strip having a plurality of individual positionsthat will be processed in various ways to form individual packagedsemiconductor devices. A position can have one or more semiconductor diewithin. The following description details exemplary embodiments ofprocesses. It will be appreciated by the person of ordinary skill havingthe benefit of this disclosure that the steps taught or claimed need notbe performed in the order shown. The process steps are able to beperformed in an order that is not inconsistent with the teachings hereinto achieve a desired end result.

FIG. 2 shows two portions of leadframe matrices 200. The first is aportion of a leadframe matrix 210 that has been selectively etched fromboth the top and bottom surfaces. The perimeter of the matrix 211 is notetched and remains at full metal thickness with a nickel/Palladium/Goldcoating to prevent corrosion. As will be shown later in a process ofassembling individual packaged semiconductor devices, the perimeter 210can be discarded in some applications. A cross section of the matrix 210taken across the line A-A the portion of the matrix 210 having a fullthickness and the portions that are etched from the bottom surface 215and portions that are etched from the top surface 225. The various voidsand cavities are able to be formed on the top or bottom surface of thematrix 210 to provide differing specific applications. Alternatively,the leadframe matrix 220 is etched from the top surface only. The etchedportions 225 are visible in the cross section taken across the line B-Bas forming cavities and voids 230. Such partially etched leadframes arereferred to herein as half etched leadframes. In some embodiments, thehalf etched leadframe 200 is mounted to a carrier tape 230 to secure itduring processing as shown in FIGS. 4A-4D and 5A-5D.

FIG. 3A shows a process of forming a molded half etched leadframe 350.The half etched leadframe 300 in this example has been etched on both atop and a bottom surface. The half etched leadframe 300 is mounted to atape carrier 305. The half etched leadframe 300 and carrier tape 305 areplaced between a top mold 310 having a tape loader on the mold surface313 and a bottom mold 335. The tape loader effectuates the movement ofthe half etched leadframe 300 through the mold. In some embodiments, thetop mold 310 comprises a film gate 355. The film gate 355 encircles aperimeter of the leadframe 300 to allow the injection therein of a moldcompound 325. The mold compound 325 is fed into the film gate 355through a cavity 320. The mold compound 325 is allowed to cool and setand the molded half etched leadframe 350 is removed from the top mold310 and bottom mold 335. In some embodiments, the tape carrier 305 isleft attached to the molded half etched leadframe 350 to carry itthrough later assembly steps. The process of FIG. 3A is seen from topand isometric views in FIG. 3B. The leadframe matrix 305 is shownwithout the top mold 310. A mold pot and cull liquefies a mold compoundand distributes the mold compound through mold runners 365 to the filmgate 355. The mold pot and cull 360 and runners 365 are removed to leavethe molded half etched leadframe 350.

FIG. 3C shows an alternate embodiment of the process shown in FIG. 3A.In this alternative exemplary embodiment, the half etched leadframe 300is mounted to a tape carrier 305. The half etched leadframe 300 andcarrier tape 305 are placed between a top mold 310 having a tape loaderon the mold surface 313 and a bottom mold 335. The tape loadereffectuates the movement of the half etched leadframe 300 through themold. In some embodiments, the top mold 310 comprises a pincer gate 375.The pincer gate 375 is coupled to the leadframe 300 to effectuate theinjection therein of a mold compound 325. The mold compound 325 is fedinto the pincer gate 375 through a cavity 320. The mold compound 325 isallowed to cool and set. Then, the molded half etched leadframe 350 isremoved from the top mold 310 and bottom mold 335. In some embodiments,the tape carrier 305 is left attached to the molded half etchedleadframe 350 to carry it through later assembly steps. The process ofFIG. 3C is seen from top and isometric views in FIG. 3D. The leadframematrix 305 is shown without the top mold 310. A mold pot and cullliquefies a mold compound and distributes the mold compound through moldrunners 365 to the pincer gate 375. The mold pot and cull 360 andrunners 365 are removed to leave the molded half etched leadframe 350.Advantageously, no film gate 355 remains on the molded half etchedleadframe 350 when the pincer gate is used to deliver the mold compound.

FIG. 4 shows an alternative embodiment for the leadframe matrices ofFIG. 2. In this embodiment, the leadframe matrix 610, comprises asupport gate 620 and is etched from both a top and a bottom surface. Thesupport gate 620 is configured to allow easy flow therein of a liquifiedmold compound (not shown). Alternatively, a leadframe matrix 630comprises a vacuum pipe 640. Applying a partial vacuum to the vacuumpipe 640 further enhances the even distribution of liquified moldcompound. A leadframe matrix can comprise both the support gate 620 andthe vacuum pipe 640 for still further enhanced liquid mold compoundencapsulation.

FIG. 5A shows an process of molding a leadframe matrix 300 having asupport gate 620. The half etched leadframe 300 is mounted to a carriertape. The leadframe matrix 300 is placed between a top mold 310 having afilm gate 315 and a bottom mold 335. Mold compound 365 is injected in aliquid state into the film gate 315. Advantageously, the support gate620 is aligned with the film gate 315 to effectuate the even flowtherein of liquified mold compound 365. The top mold 310 and bottom mold335 are removed. A film gate remainder 355 is able to be removed in alater process step or discarded when individual semiconductor devicesare singulated.

FIG. 5B shows an process of molding a leadframe matrix 300 having asupport gate 620. The half etched leadframe 300 is mounted to a carriertape. The leadframe matrix 300 is placed between a top mold 310 having apincer gate 375 and a bottom mold 335. Mold compound 355 is injected ina liquid state into the pincer gate 375. Advantageously, the supportgate 620 is aligned with the pincer gate 375 to effectuate the even flowtherein of liquified mold compound 355. The mold compound 355 fills thecavities 325 in the half etched leadframe 300 to form a half etchedmolded leadframe 350. The top mold 310 and bottom mold 335 are removed.The carrier tape 305 is able to be removed in a later process step ifdesired.

FIG. 5C shows another alternative to the process described in FIG. 5A.The half etched leadframe matrix 300 having a vacuum pipe 640 is mountedto a carrier tape 305. The leadframe matrix 300 is placed between a topmold 310 and a bottom mold 335. In this embodiment, the top mold 310comprises a vacuum exhaust 646. When mold compound 365 is pumped inthrough the film gate 315, a partial vacuum is formed at the vacuumexhaust 646 to effectuate the more even distribution of the moldcompound 365 into the cavities 325 of the half etched leadframe 300.

FIG. 5D shows another alternative to the process described in FIG. 5B.The half etched leadframe matrix 300 having a vacuum pipe 640 is mountedto a carrier tape 305. The leadframe matrix 300 is placed between a topmold 310 and a bottom mold 335. In this embodiment, the top mold 310comprises a vacuum exhaust 646. When mold compound 365 is pumped inthrough the pincer gate 375, a partial vacuum is formed at the vacuumexhaust 646 to more evenly distribution of the mold compound 365 intothe cavities 325 of the half etched leadframe 300. A more ideal vacuumis able to be formed with equipment configured to create larger negativepressures as required by specific applications that do not deviate fromthe teachings of this disclosure.

FIG. 6 shows a process 400 of applying the half etched leadframe 405.The half etched leadframe 405 is mounted to a carrier tape 406 fortransport through the process. It will be appreciated that manycommercially available machines are able to carry out the stepsdescribed herein. In the next step 410, semiconductor die 415 aremounted to individual leadframe units within the leadframe matrix.Semiconductor die 415 are mounted to the leadframe units by tape oradhesive. The semiconductor die 415 are preferably placed by pick andplace automated machines. Generally, a pick and place machine comprisesa robotic arm that picks up semiconductor die that have been singulatedfrom a wafer and places them in a desired location and orientationwithin an individual leadframe unit. In some applications, multiple dieare placed in a leadframe unit. These multiple die are able to be sideby side or stacked on top of each other as applications require. Also,wire bonds 417 are attached from bond pads on the semiconductor die 415to the leadframe units to effectuate electrical communication betweenthe semiconductor die and the board to which the finished product willbe mounted to. Next, in a step 420, the half etched leadframe 405 ismolded in a process such as the ones described in FIGS. 3A-3D. Thecarrier tape 406 is removed in a step 430. The molded leadframe is movedto a sawing step 440 where saws 445 singulate the leadframe matrixthereby forming individual semiconductor devices 450.

An alternative application is shown in FIG. 7. The process 500 startswith a half etched leadframe 505 mounted to a carrier tape 508. In thenext step 510, the half etched leadframe is filled with a first moldcompound 515 in one of the processes described in FIGS. 3A-3D. In thenext step 520, the carrier tape 508 is removed. In the step 530,semiconductor die 535 are mounted to individual leadframe units. In someembodiments, the die 535 are electrically coupled to the leadframe 505by wirebonds 538. In a step 540, a second mold compound 545 is used toencapsulate the leadframe having the semiconductor devices 535. Theleadframe matrix 505 is singulated by saw blades 555 in a step 540,thereby forming individual semiconductor devices 565 in a final step550. The half etched leadframe technique of FIGS. 3A-3D is able to beused to make a thin profile semiconductor package 450 as described inFIG. 4 or a thicker profile package 550 of FIG. 5.

1. A system for forming singulated semiconductor devices comprising: a.a top mold comprising an injector for injecting a mold compound in aliquid state; and b. a bottom mold configured to hold a leadframe matrixto receive the mold compound in a liquid state thereby forming a moldedleadframe matrix; c. a pick and place mechanism for placingsemiconductor die in individual leadframe units; and d. at least onecutting element for singulating the molded leadframe matrix therebyforming singulated semiconductor devices.
 2. The system for formingsingulated semiconductor devices according to claim 1 wherein theinjector comprises a film gate.
 3. The system for forming singulatedsemiconductor devices according to claim 1 wherein the injectorcomprises a pincer gate.
 4. The system for forming singulatedsemiconductor devices according to claim 1 further comprising a tapecarrier for carrying the leadframe units.
 5. The system for formingsingulated semiconductor devices according to claim 1 wherein the atleast one cutting element comprises a saw.
 6. The system for formingsingulated semiconductor devices according to claim 1 wherein the atleast one cutting element comprises a punch.
 7. The system for formingsingulated semiconductor devices according to claim 1 wherein theinjector comprises a pincer gate.
 8. The system for forming singulatedsemiconductor devices according to claim 1 wherein the injectorcomprises a film gate.
 9. The system for forming singulatedsemiconductor devices according to claim 1 further comprising a vacuumpump output.